Currently, fuel cell systems use a polymer electrolyte membrane (PEM) having a polymer that requires the presence of water to transport protons harvested from hydrogen through the membrane. The water which is required for conduction of protons through the membrane is delivered to the membrane via humidified air and hydrogen gas streams. Insufficient humidification of the air and hydrogen streams leads to drying of the membrane, resulting in higher resistance to ion flow and reduced fuel cell performance. On the other hand, excessive humidification of the air and hydrogen streams can result in accumulation of water in the GDL (gas diffusion layer) of a fuel cell stack, resulting in flooding and covering of the active catalysts in the fuel cell membranes. This also reduces fuel cell performance. Therefore, humidity measurement would be beneficial in the air and hydrogen gas streams of a fuel cell system to measure the humidity of the air or gas, respectively.
Today's state-of-the-art humidity sensor technology typically does not provide a robust humidity measurement within a bi-phasic environment. For example, during a cold start of a fuel cell system, unprotected humidity sensors become saturated and report inaccurate readings as a result of liquid water contacting the humidity sensor. This occurs because the sensor is located in a condensing environment that contains high levels of liquid water.